Compositions comprising an epoxy resin and mercaptan-containing polyphenols

ABSTRACT

Compounds of formula I or II ##STR1## in which formulae R 1  and R 2  are each independently of the other hydrogen, alkyl, alkenylmethyl, cyclohexyl, phenyl, benzyl or tolyl, or are a --CH 2  --CHR 3  --CH 2  --S--H group, R 3  and R 4  are each independently of the other hydrogen or methyl, X is alkylene, --S--, --SO--, --SO 2  -- or substituted alkylene, R 5  and R 6  are each independently of the other hydrogen or alkyl, R 8  is hydrogen, alkyl, alkenylmethyl or phenyl, and wherein n is an integer from 1 to 10, can be used as hardeners for epoxy resins. 
     The compositions containing epoxy resins and these hardeners are particularly suitable for use as adhesive formulations. The cured products have good moisture resistance.

This is a divisional of application Ser. No. 003,962 filed on Jan. 16,1987 now U.S. Pat. No. 4,721,814.

The present invention relates to compounds containing at least twomercaptan radicals and phenolic hydroxyl groups, to compositionscontaining a curable epoxy resin and said compounds, to the curedproducts which can be obtained therefrom and to the use of the curablecompositions as adhesives.

Epoxy resins are well known in the art and are reacted with a wide rangeof different hardeners to form cured products.

Bismercaptan hardeners are konwn. As a rule, these compounds are acitveeven at room temperature. For many applications a curing reaction whichcan be carrried out under controlled temperature conditions isdesirable. In accordance with the present invention, this can beachieved by employing a mercaptan hardener containing a second, lessreactive, phenolic hydroxyl group in the molecule.

The cured product adheres particularly well to metals and has very goodmoisture resistance.

Mercaptpropylphenols are known from U.S. Pat. No. 3,336,393 aspesticides. No mention of the use thereof as hardeners for epoxy resinsis made in said patent specification. Moreover, the known compounds aremononuclear monophenols.

The present invention relates to compounds of formula I or II ##STR2##in which formulae R¹ and R² are each independently of the otherhydrogen, C₁ -C₁₈ alkyl, C₃ -C₁₈ alkenylmethyl, cyclohexyl, phenyl,benzyl or tolyl, or are a --CH₂ --CHR³ --CH₂ --S--H group, R³ and R⁴ areeach independently of the other hydrogen or methyl, X is --CR⁵ R⁶ --,--S--, --SO--, --SO₂ -- or --(CH₃)C[--(CH₂)_(m) --COOR⁷ ]--, R⁵ and R⁶independently of the other hydrogen or C₁ -C₆ alkyl, R⁷ is C₁ -C₁₈-alkyl, R⁸ is hydrogen, C₁ -C₁₈ alkyl, C₃ -C₁₈ alkenylmethyl or phenyl,m is 1 or 2 and n is an integer from 1 to 10.

R¹, R², R⁷ and R⁸ as C₁ -C₁₈ alkyl are straight chain or branchepreferably straight chain, radicals. Illustrative of such radicals aremethyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tertbutyl,n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-dodecyl,n-tetradecyl, n-hexadecyl or n-octadecyl, as well as1,1,3,3-tetramethylbutyl or 2-ethylhexyl.

Short and straight chain C₁ -C₆ alkyl radicals are preferred, withmethyl being most preferred.

R⁵ and R⁶ as C₁ -C₆ alkyl may be e.g. methyl, ethyl, n-propyl, n-butyl,n-pentyl or n-hexyl, with methyl being preferred.

R¹, R² and R³ as C₃ -C₁₈ alkenylmethyl radicals are straight chain orbranched, preferably straight chain. Examples of such radiicals areallyl, but-3-enyl, pent-4-enyl, hex-5-enyl, oct-7-enyl, dec-9-enyl,dodec-11-enyl or octadec-17-enyl, with allyl being preferred.

Preferred compounds of formulae I and II are those wherein R³ and R⁴ arehydrogen.

Particularly interesting compounds of formula I are those wherein R¹ andR² are each independently of the other hydrogen or C₁ -C₁₂ alkyl, R³ andR⁴ are hydrogen, X is a --CR⁵ R⁶ --group, and wherein R⁵ and R⁶ are eachindependently of the other hydrogen or methyl.

Interesting compounds of formula I are also those wherein R¹, R², R³ andR⁴ are hydrogen, and X is a group selected from --CH₂ --, --CH(CH₃)or--C(CH₃)₂ --.

Particularly preferred compounds of formula I are those wherein R¹ andR² are each independently of the other a --CH₂ --CHR³ --CH₂ --S--Hgroup.

Of special interest are also compounds of formula II, wherein R³ ishydrogen, R⁸ is hydrogen or methyl, --CR⁵ R⁶ -- is a group selected from--CH₂ --, --CH(CH₃)-- or --C(CH₃)₂ --, and wherein n is an integer from1 to 4

The --CH₂ --CHR³ --CH₂ --S--H groups in the novolak of formular II arepreferably in ortho- or para-position with respect to the phenolichydroxyl group; most preferably in the ortho- position.

R¹ and R² are preferably hydrogen or methyl, with hydrogen being mostpreferred.

R⁸ is preferably hydrogen.

X is preferably --CH₂ -- or --C(CH₃)₂ --, with --C(CH₃)₂ -- being mostpreferred.

Further preferred meanings of the group X are --S-- or --SO₂ -- or 13(CH₃)C[--CH₂ --COOCH₃ ]13 or --(CH₃)C[--CH₂ --CH₂ --COOCH₃ ]--.

The compounds of formula I or II can for example be prepared by reactinga compound of formula III or IV ##STR3## with a molar amount of athiocarboxylic acid of formula V ##STR4## which is substantiallyproportionate to the content of allylic double bonds, in the presence ofa free radical generator followed by a saponification step. In theformulae III, IV and V above, R¹, R², R³, R⁴, R⁵, R⁶, R⁸ and X, as wellas the index n, have the meanings as defined above, and R⁹ is amonovalent organic radical, e.g. alkyl, preferably methyl; however, inthis case R¹ and R² are --CH₂ --CR³ =CH₂ instead of --CH₂ --CHR³ --CH₂--S--H.

If compounds of formula I or II containing alkenylmethyl radicals R¹, R²or R⁸ are to be prepared, then the compounds of formula III or IV arereacted with a corresponding deficiency of thiocarboxylic acids offormula V.

The novolak of formula IV may also contain small proportions of phenolnuclei which do not contain allyl, e.g. phenol, o-cresol or p-cresolnuclei.

The reaction products (acylthiopropyl derivatives) of formulae VI andVII ##STR5##

A= ##STR6## are converted into the mercaptophenols of formulae I and IIin a subsequent hydrolysis step in a manner known per se.

The hydrolysis is conveniently effected in a manner known per se underalkaline conditions, for example under the action of aqueous KOH. Thecompounds of formulae I and II may also be prepared without having toeffect said hydrolysis step, i.e. by reacting the compounds of formulaIII or IV direct with hydroge sulfide in the presence of a free radicalgenerator. Both variants of reactions of this type are described in U.S.Pat. No. 3,336,393.

The bis- or polyallylphenols and bis- or polymethallylphenols of formulaIII or IV are known compounds or they can be prepared by methods whichare known per se, for example by etherification of the correspondingpolyphenols with allyl halide and subsequent Claisen rearrangement.

The thiocarboxylic acids of formula V are also known compounds and canlikewise be obtained by methods which are known per se. A preferredprocess comprises reacting a suitable carboxylic acid anhydride,preferably acetic anhydride, with hydrogen sulfide in alkaline aqueoussolution, isolating the resultant mixture of carboxylic acid andthiocarboxylic acid and using it, without further separation, in thesubsequent reaction with the allylphenol or methylallylphenol.

The amount of thiocarboxylic acid V or hydrogen sulfide employed willdepend on the number of allyl or methallyl groups in the startingmaterial III or IV. As a rule, equimolar amounts of thiocarboxylic acidor hydrogen sulfide are used, based on the allyl groups. However, it isentirely possible to use an excess or a less than equivalent amount ofthiocarboxylic acid.

Use of a less than equivalent amount of thiocarboxylic acid V willresult in only a partial reaction of the allyl groups of compounds IIIor IV. Such partially thioacylated products, especially partiallyreacted novolaks IV are also suitable as intermediates for thepreparation of mercaptophenols of the invention. The resultant finalproducts also fall within the scope of this invention. These partiallyreacted novolaks IV are mixtures of compounds of different chain lengthand differing mercapto group content. On average, at least 50% of theallyl groups of compounds III and IV should be reacted.

The reaction to give the final product I or II or the intermediate VI orVII is induced by radical initiation. This radical initiation isachieved e.g. by exposing the reaction mixture, if desired in thepresence of a catalyst, to irradiation with shortwave light, or byheating the mixture, preferably in the presence of a free radicalgenerator.

Illustrative of free radical generators are organic peroxides such asbenzoyl peroxide, acetyl peroxide or cumyl hydroperoxide and, inparticular, azo compounds. Preferred azo compounds are in particularthose in which the azo group is attached on both sides to tertiarycarbon atoms which, in addition to carrying alkyl groups, also carrynitrile or ester groups. An important representative of this class ofcompound is thus e.g. a,a-azobisisobutyronitrile (AIBN).

Exemplary of catalysts which may, if desired, be suitably used for thephotoinitiation reaction are benzoin ethers, benzile ketals,ω-dialkoxyacetophenone derivatives or aromatic ketone/aminecombinations.

The amount of free radical generator which may be employed is notcrucial and may vary within wide limits. It is preferably less than 10mol % of the number of allyl or methallyl groups in the reactionmixture.

The reaction of compound III and V or IV and V or of compound III or IVwith hydrogen sulfide can be carried out in the presence or absence of asolvent.

If a solvent is employed, it must be inert to the reactants and able todissolve them. Examples of suitable solvents are therefore aliphatic oraromatic hydrocarbons such as hexane, benzene, toluene or xylene; orchlorinated hydrocarbons such as dichloromethane or chlorobenzene; andalso ethers such as dioxane or diethyl ether; or aprotic solvents suchas dimethylformamide. Depending on the mode of reaction and on thereactants, the reaction temperature is normally in the range from -10°to 250° C.

It is preferred to carry out the reaction of the allylphenol with thethiocarboxylic acid in the temperature range from 40° to 80° C. in aninert gas, for example N₂, in the absence of a solvent. The radicalgenerator employed in this process variant is preferablyazobisisobutyronitrile, although other radical generators are alsosuitable for the purpose. Subsequently, hydrolysis is effected withaqueous potassium hydroxide solution.

The phenols of this invention can be isolated from the reaction mixturein conventional manner, for example by distillation or fractionalcrystallation or by extraction, preferably with an aqueous alkalinesolution.

The compounds of formula I and II can be employed as hardeners for epoxyresins.

Accordingly, the invention also relates to compositions comprising

(a) an epoxy resin containing on average more than one epoxy group inthe molecule or a still fusible and/or soluble curable precondensate ofsaid epoxy resin, and

(b) at least one compound of formula I and/or II, and

(c) optionally, curing accelerators,

and to the cured products which can be obtained therefrom by heating.

Preferred compositions are those comprising (a) the epoxy resin and (b)at least one compound of formula I.

The epoxy resins to be employed preferably contain more than one epoxygroup in the molecule. Such compounds are in particular:

alicyclic polyepoxides such as epoxyethyl-3,4-epoxycyclohexane,(vinylcyclohexene diepoxide), limonene diepoxide, dicyclopentadienediepoxide, bis(3,4-epoxycyclohexylmethyl) adipate,(3',4'-epoxycyclohexylmethyl)-3,4-epoxycyclohexanecarboxylate,3',4'-epoxy-6'-methylcyclohexylmethyl-3,4-epoxy-6-methylcyclohexanecarboxylate,3-(4',4'-epoxycyclohexyl)-2,4-dioxaspiro[5,5]-8,9-epoxyundecane,3-(glycidyloxyethoxyethyl)-2,4-dioxaspiro-[5.5]-8,9-epoxyundecane;

di- or polyglycidyl ethers of polyhydric aliphaic alcohols such as1,4-butanediol, or polyalkylene glycols such as polypropylene glycols;di- or polyglycidyl ethers of cycloaliphatic polyols such as2,2-bis(4-hydroxycyclohexyl)propane; di- or polyglycidyl ethers ofpolyhydric phenols such as resorcinol, bis(4-hydroxyphenyl)methane(bisphenol F), 2,2-bis(4-hydroxyphenyl)propane (bisphenol A),2,2-bits(4'-hydroxy-3',5'-dibromophenyl)propane,1,1,2,2,-tetrakis(4'-hydroxyphenyl)ethane, or condensates of phenolswith formaldehyde which are obtained under acid conditions, such asphenol novolaks and cresol novolats; and also di- orpoly(8-methylglycidyl)ethers of the above polyalcohols and polyphenols;

polyglycidyl esters and poly(β-methylgl) esters of polyvalent carboxylicacids such as phthalic acid, terephthalic acid, tetrahydrophthalic acidor hexahydrophthalic acid;

N-glycidyl derivatives of amines, amides and heterocyclic nitrogen basessuch as N,N-diglycidyl aniline, N,N.-diglycidyl toluidine,N,N,N',N'-tetraglycidyl bis(4-aminophenyl)methane, triglycidylisocyanurate, N,N'-diglycidyl ethyl urea,N,N'-diglycidyl-5,5-dimethylhydantoin,N,N'-diglycidyl-5-isopropylhydantoin,N,N'-diglycidyl-5,5-dimethyl-6-isopropyl-5,6-dihydrouracil.

Particularly preferred are polyglycidyl ethers of phenol/formaldehyde orcresol/formaldephyde novolaks as well as diglycidyl ethers of bisphenolA and bisphenol F.

Examples of suitable catalysts (accelerators) are basic organiccompounds such as primary and/or secondary amines, e.g.N,N-dimethyl-1,7-diamino-4-azaheptane, or tertiary amines, salts orquaternary ammonium compounds thereof, e.g. benzyl dimethylamine,2,4,6-tris(dimethylaminomethyl)phenol, 1-methylimidazole,2-ethyl-4-methylimidazole, 2-phenylimidazole, 4-aminopyridine,tripentylammonium phenolate; or alkali metal alcoholates, e.g. sodiumhexane triolate.

In particular in combination with strong organic bases such astetrabutylammonium hydroxide, the compounds of formulae I and II can beemployed for curing epoxy resins at low temperatures.

The reaction (curing) of the compositions of the invention isconveniently carried out in the temperature range from -25° C. to 200°C., preferably from 25° C. to 180° C.

Preferred curing catalysts are 2-phenylimidazole,N,N-dimethylbenzylamine or 2,4,6-tris(dimethylaminomethyl)phenol.

Curing can be carried out in known manner in two or more steps, thefirst step being carried out at low temperature (room temperature) andthe postcuring at more elevated temperature.

Two-step curing is normally carried out by first discontinuing thecuring reaction prematurely, i.e. performing the first step at roomtemperature or slightly elevated temperature, when a still fusibleand/or soluble curable precondensate (B-stage) is obtained from theepoxy component (a) and the hardener component (b). Such a precondensatecan be used e.g. for making prepregs, moulding compounds or sinteringpowders.

The compositions of this invention comprising a) an epoxy resincontaining on average more than one epoxy group in the molecule, (b) atleast one compound of formula I or II form soluble B-stages if theseresin/hardener compositions are stored at room temperature. Suchcompositions are storage stable over prolonged periods of time (days)and can thus be further processed in suitable manner.

The term "curing" as employed throughout this specification denotes theconversion of the soluble, either liquid or fusible, epoxy resins intosolid insoluble and infusible three-dimensional crosslinked products ormoulding materials, usually with concomitant shaping to moulded articlessuch as castings, mouldings and laminates, impregnations, coatings,varnish films or bonds.

The compositions of this invention can be prepared by simple stirring ofthe components and cautiously warming the components until dissolved. Ifa solid epoxy resin is used, this is temporarily heated to the melt andthen the hardener and, optionally, the curing accelerator and/or otheradditives are dissolved in the melt.

Customary modifiers such as extenders, fillers and reinforcing agents,pigments, dyes, plasticisers, flow control agents, thixotropic agents,flexibilisers, flame retardants or mould release agents, can also beadded, in any phase, to the curable mixtures of the present inventionbefore curing.

Typical examples of extenders, reinforcing agents, fillers and pigmentswhich may be added to the curable mixtures of this invention are: coaltar, bitumen, liquid coumarone/indene resins, textile fibres, glassfibres, asbestos fibres, boron fibres, carbon fibres, cellulose,polyesters, polyamides, polyethylene powder, polypropylene powder, woodpowder, quartz powder, mineral silicates such as mica, asbestos powder,slate powder, kaolin, silica aerogel, lithopones, barytes, titaniumdioxide, carbon black, graphite, oxide colours such as iron oxide, ormetal powders such as aluminium powder or iron powder.

Examples of suitable plasticisers for modifying the curable compositionsare dibutyl phthalate, dioctyl phthalate and dinonyl phthalate,tricresyl phosphate, trixylenyl phosphate and diphenoxyethylformal.

Examples of flow control agents which can be added when the curablemixtures are used in particular in surface protection are silicones,liquid acrylic resins, cellulose acetobutyrate, polyvinylbutyrate, waxesor stearates (some of which are also used as mould release agents).

Examples of suitable flexibilisers are oligoester segments, polyesters,thermoplasts and butadiene/acrylonitrile oligomers such as Hycar® (aproduct of Goodrich).

The curable mixtures of this invention are distinguished by goodadhesion to metals, high deflection temperatures and also goodresistance to moisture and chemicals.

The curable mixtures of this invention are used, in particular, in thefields of surface protection, electrical engineering, laminatingprocesses and adhesives technology and in the building trade. They canbe used in a formulation suited in each case to the particularapplication, in the unfilled or filled state, if desired in the form ofsolutions or emulsions, as paints, solvent-free coatings, whirlsintering powders, moulding compositions, injection mouldingcompositions, impregnating resins, casting resins, foams, adhesives,films, sheets, bonding agents, tooling resins, laminating resins,sealing and trowelling compounds, flooring compositions, and as bindersfor mineral aggregates.

In particular, the present invention relates to the use of compositionscontaining a) an epoxy resin comprising on average more than one epoxygroup in the molecule, and b) at least one compound of the formula Iand/or II as adhesives.

PREPARATORY EXAMPLES 1. Preparation of2,2'-bis(3-(3-mercaptopropyl-4-hydroxyphenyl)propane

(1a) o,o'-Bis(3-acetylthiopropyl) bisphenol A

666.8 g of 2,2-bis(3-allyl-4-hydroxyphenyl)propane are placed in areaction vessel equipped with a stirrer, dropping funnel and N₂ inletand heated to 75° C. under N₂ gas. 4.92 g of azobisisobutyronitrile(AIBN) are then added and, through the dropping funnel, 780 g thioaceticacid are added over one hour. The temperature of the reaction mixture ismaintained at 75° C. and 3 further 4.92 g portions ofazobisisobutyronitrile are added every 20 minutes until a total of 19.68g of AIBN has been added. The mixture is stirred at 75° C. under N₂ for4 hours. A final portion of 4.92 g of azobisisobutyronitrile is addedand the mixture is stirred for a further 3 hours. The product is thenevaporated in a rotation vacuum evaporator (rotavap) to give 1036 g of ayellow paste.

    ______________________________________                                        (a) Elementary analysis:                                                              C           H      S                                                  ______________________________________                                        theory %  65.19         7.00   13.92                                          found %   64.5          6.96   13.2                                           ______________________________________                                    

(b) 100 MHz ¹ H-NMR spectrum: Absence of olefinic proton peaks in the5-6 ppm region (standard: TMS) indicate the complete disappearance ofthe allylic group

Peaks at:

2.3 ppm (3 protons; --S--CO--CH₃)

1.8 ppm (2 protons; --S--C13 CH₂ --C--phenyl)

2.6 ppm (2 protons; --S--CH₂ --C--C-phenyl)

2.8 ppm (2 protons; --S--C--C--CH₂ --phenyl).

(1b) Purification of the crude product of Example (1a)

360.8 g of the crude pasty product of Example 1a) are dissolved in 100ml of hot xylene. 1 g of active charcoal is added and the solution isfiltered and allowed to crystallize at 5° C. The crystals are filteredand dried under vacuum at 100° C. (50 mbar), affording 142 g of whitecrystals having a melting point of 118.1°-119.5° C.

    ______________________________________                                        Elementary analysis:                                                                     C    H          S      O                                           ______________________________________                                        calculated % 65.19  7.00       13.92                                                                              13.89                                     found %      65.88  7.07       13.43                                                                              13.79                                     ______________________________________                                    

(1c) o,o'-Bis(3-mercaptopropyl) bisphenol A

50 g of the product of Example (1a), purified in accordance with Example(1b), are added to a solution of 44.1 g of KOH in 200 ml of a mixture ofethanol and water (50:50 parts by volume). The mixture is kept at 50° C.for 1 hour and then boiled under reflux for 1 hour at about 80° C. Afterthe mixture has cooled to room temperature, it is adjusted to a pH of6-7 with 37.5% hydrochloric acid and extracted with 1 l ofdichloromethane. The organic phase is separated and dried over sodiumsulfate, and the solvent is drawn off in a rotation evaporator to give36.4 g of a slightly yellow resinuous liquid (yield: 38.9% of theory,based on acylated product).

Analytical data

    ______________________________________                                        (a) Elementary analysis                                                                       C    H                                                        ______________________________________                                        calculated %      66.98  7.49                                                 found %           67.2   7.42                                                 ______________________________________                                    

(b) Thiol content (determined by iodometric titration)

4.60 --SH equivalents/kg

(c) ¹ H-NMR spectrum (250 MHz)

    ______________________________________                                        6.5-7     ppm (m)     6 aromatic protons                                      5.2       ppm (s)     2 phenolic protons                                      2.5-2.9   ppm (m)     8 aliphatic protons                                                           (--CH.sub.2 --CH.sub.2 --phenyl)                        1.75-2.1  ppm (m)     4 aliphatic protons                                                           (--C--CH.sub.2 --S--)                                   1.6       ppm (s)     6 aliphatic protons                                                           (--C(CH.sub.3).sub.2 --)                                1.4       ppm (m)     2-thiol protons                                         ______________________________________                                    

2. Preparation of a novolak based on formaldehyde and2-mercaptopropylphenol

2a) Preparation of an (o-acetylthiopropyl)phenol/formaldehyde novolak

Following the procedure of Example 1a), 419.9 g of a2-allylphenol/formaldehyde novolak (prepared by condensation of 1 partof formaldehyde with 6 parts of 2-allylphenol; allyl group content: 2.36val) are reacted at 80° C., under nitrogen, with 179.9 g (2.36 moles) ofthioacetic acid and 10.2 g of azobisisobutyronitrile. Theazobisisobutyronitrile is added in 5 equal portions of 2.04 g. Yield:589.2 g of product (98.2% of theory).

The ¹ H-NMR peaks (250 MHz) of the allyl protons of the startingmaterial in the 5.1-5.2 ppm and 5.9-6.1 ppm range (against TMS) havedisappeared from the ¹ H-NMR spectrum of the final product. Instead apeak of the protons of the acetyl group appears (at 2.3 ppm).

(2b) Purification of the crude product

200 ml of dichloromethane and 220 ml of aqueous ethanol (water content:30% by volume) are added to 177.2 g of the crude product of Example (2a)and the supernatant phase is removed by decantation. A further 220 ml ofaqueous ethanol and 100 ml of water are added and again the supernatantphase is removed by decantation. The residual novolak is washed with two230 ml portions of water and dried over Na₂ SO₄. The product issubsequently dried again at 40° C. (17 mm Hg) and at 60° C. (3 mm Hg) ina rotary evaporator. Yield: 164 g of purified final product. Asdetermined by GPC, said product has molecular weights of 527 (numberaverage) and 597 (weight average) respectively.

(2c) Saponification of the acetylated product to give mercaptan

50 g of the product of Example (2a), purified in accordance with Example(2b), are placed in a reaction vessel. A solution of 22.4 g (0.4 mol) ofpotassium hydroxide in 200 ml of a mixture of ethanol and water (50:50parts by volume) is added. The mixture is allowed to react for about11/2 hours at 50° C. and is subsequently boiled under reflux for 2hours. After the mixture has cooled to room temperature, it isneutralised with 15 ml of 37.5% hydrochloric acid. The precipitate isisolated by filtration, extracted with 350 ml of dichloromethane anddried over Na₂ SO₄. After filtration, the solvent is drawn off,affording 37.65 g of a viscous resinuous product.

Mercaptan content

(titrimetrically determined):

4.04 equiv./kg

(theory: 4.07 equiv./kg).

Molecular weight

(determined by GPC analysis):

M_(n) =484;

M_(n) =569.

APPLICATION EXAMPLES Example A

An adhesive formulation consisting of 100 parts by weight of a liquidepoxy resin based on bisphenol A (epoxide value: 5.25 val/kg), 49.8parts by weight of the hardener of Example (1c) and 0.02 parts by weightof 2-phenylimidazole as curing accelerator is prepared by mixing thecomponents at 60° C.

Adhesive bonds are then prepared with this formulation between aluminumsurfaces. This is done by punching bore holes of a specific diameter andspecific depth in an aluminum plate and filling them with the resinmixture. Aluminum cylinders of specific diameter are then fixed on thissubstrate.

The adhesive bonds are then cured for 2 hours at 120° C., 2 hours at150° C. and 2 hours at 180° C.

Measurement of the adhesive bond is made with a Twistometer (q.v.Adhesion 3, edited by K.W. Allen; Applied Science Publishers Ltd.;Barking (Essex); 1978).

To this end the aluminium base plate is made fast and a specifictorsional force is exerted on the aluminium cylinder by means of a leverarm. The adhesion can be ascertained from the maximum torsional forceresulting in rupture of the adhesive bond.

An adhesion of 70.1 N/mm² is measured.

Example B

An adhesive formulation consisting of 100 parts by weight of liquidepoxy resin (diglycidyl ether based on bisphenol A; epoxide content: 5.3val/kg), 41.8 parts by weight of 2,2'-bis(3-mercaptopropyl)bisphenol Aaccording to Example 1c) and 2.2 parts by weight ofN,N-dimethyl-1,7-diamino-4-azaheptane as curing accelerator is preparedby mixing the components at room temperature. Al/Al bonds are thenprepared with this formulation. The adhesive bonds are cured bysubjecting them to heat for 30 minutes at 180° C.

As a criterion of the quality of the adhesive bond, the shear strength(on Anticorodal B) is determined in accordance with DIN 53283. A valueof 22.4 N/mm² is measured.

Example C

An adhesive formulation consisting of 100 parts by weight of liquidepoxy resin (diglycidyl ether based on bisphenol A; epoxide content: 5.3val/kg), 44.0 parts by weight of 2,2'-bis(3-mercaptopropyl)bisphenol Aaccording to Example (1c) and 0.25 parts by weight of 2-phenylimidazoleas curing accelerator is prepared by mixing the components at 60° C.

Al/Al bonds are then prepared with this formulation. The curing of theadhesive bonds and the measurement of the shear strength are carried outin accordance with the procedure described in Example B. A shearstrength of 8.6 N/mm² is measured.

What is claimed is:
 1. A composition comprising(a) an epoxy resincontaining on average more than one epoxy group in the molecule, and (b)a compound of formula I or II ##STR7## in which formulae R¹ and R² areeach independently of the other hydrogen, C₁ -C₁₈ alkyl, C₃ -C₁₈alkenylmethyl, cyclohexyl, phenyl, benzyl or tolyl, or are a --CH₂--CHR³ --CH₂ --S--H group, R³ and R⁴ are each independently of the otherhydrogen or methyl, X is --CR⁵ R⁶ --, --S--, --SO--, --SO₂ -- or--(CH₃)C[--(CH₂)_(m) --COOR⁷ ]--, R⁵ and R⁶ are each independently ofthe other hydrogen or C₁ -C₆ alkyl, R⁷ is C₁ -C₁₈ - alkyl, R⁸ ishydrogen, C₁ -C₁₈ alkyl, C₃ -C₁₈ alkenylmethyl or phenyl, m is 1 or 2and n is an integer from 1 to 10, or a mixture of such compounds.
 2. Acured product obtainable by heating a composition as claimed in claim 1.